<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Promise 封装 AJAX</title>
    <link crossorigin='anonymous' href="https://cdn.bootcss.com/twitter-bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
    <div class="container">
        <h2 class="page-header">Promise 封装 AJAX 操作</h2>
        <button class="btn btn-primary" id="btn">点击发送 AJAX</button>
    </div>
    <script>
        //接口地址 https://api.apiopen.top/getJoke
        //获取元素对象
        const btn = document.querySelector('#btn');

        btn.addEventListener('click', function(){
                
                //调用then方法
                var p =  {
                    resolve: value=>{
                        console.log(value);
                    },
                    reject: reason=>{
                        console.warn(reason);
                    }
                };

                //1.创建对象
                const xhr = new XMLHttpRequest();
                //2. 初始化
                xhr.open('GET', 'https://api.apiopen.top/getJoke');
                //3. 发送
                xhr.send();
                //4. 处理响应结果
                xhr.onreadystatechange = function(){
                    if(xhr.readyState === 4){
                        //判断响应状态码 2xx   
                        if(xhr.status >= 200 && xhr.status < 300){
                            //控制台输出响应体
                            p.resolve(xhr.response);
                        }else{
                            //控制台输出响应状态码
                            p.reject(xhr.status);
                        }
                    }
                }
        
        });
    </script>
</body>
</html>